For unknown reason after the plugin finds no translation for the current locale, in my case Bulgarian (bg_BG) it overrides the wordpress $locale variable, used as global one (may be) for whole system locale.

The overridden value is others, so any other plugins loaded after this one assume to search domain-others.mo files, which do not exist. This issue brakes proper work of WordPress, practically get_locale and plugin_load_textdomain, because of wrong, overridden value in $locale, so any other plugin translations will not work.

Summary: I have spent some time in debugging what is wrong with WordPress, and when I saw no problem source in WordPress core files plus the list of several plugins, first of which (before this one) were trying to load correct files, I had located this bug.